Radiation image sensors, which convert radiation into electrical signals and enable electrical processing of the signals, are used widely in medical and industrial fields. The acquired electrical signals can be processed electrically and displayed on a monitor. A representative example of such a radiation image sensor is a radiation image sensor that uses a scintillator material for converting radiation in to light. With this type of radiation image sensor, an image pickup device, for further conversion of the converted light into electrical signals, is used in combination. For example, a MOS type image sensor, etc., is used as the image pickup device. For use in medical fields and non-destructive inspections (especially inspections using a micro-focused X-ray source, etc.), the irradiation dose of radiation is limited, and thus a radiation image sensor of high sensitivity that enables a high optical output with the limited irradiation dose is desired.
FIG. 9 is a longitudinal sectional view of a radiation image sensor described in International Patent Publication No. WO99/66345 (referred to hereinafter as “Prior Art 1”). To form this radiation image sensor 4, a scintillator panel 8, comprising a substrate 50, a light reflecting film 60, formed on the substrate 50, and a scintillator 10, formed on the light reflecting film 60, is combined with an image pickup device 20, which is disposed so as to face the scintillator 10. Radiation 30 enters from the substrate 50 side, passes through the light reflecting film 60, and is converted into light at the scintillator 10. The light resulting from conversion is received by the image pickup device 20 and converted into electrical signals. The light reflecting film 60 has a function of reflecting the light emitted by the scintillator 10 and returning this light to the scintillator 10 side to thereby increase the amount of light entering the light receiving part of the image pickup device 20. A film of metal, such as aluminum, etc., is mainly used as the light reflecting film 60.
FIG. 10 is a longitudinal sectional view of a radiation imaging device described in JP 5-196742A (referred to hereinafter as “Prior Art 2”). This radiation imaging device 3 comprises a substrate 51, a light detector 21, which is disposed on the substrate 51 and serves as an image pickup device, a scintillator 10, formed on the light detector 21, a thin film 41, disposed on the scintillator 10, a light reflecting film 70, formed on the thin film 41, and a moisture sealing layer 42, formed on the light reflecting film 70. This arrangement differs largely from that of the Prior Art 1 in that the light detector 21 is used as a base member for fixing and supporting the scintillator 10 and the light reflecting film 70 is formed above the scintillator 10 across the thin film 41. The thin film 41 is formed of an organic or inorganic material and absorbs the non-uniformity on the scintillator 10 to make the light reflecting film 70 uniform in reflectance. This publication indicates that a dielectric multilayer film, arranged from TiO2 and SiO2, etc., which differ mutually in optical refractive index, may be used as the light reflecting film 70.